Starvation reduces renal pyruvate dehydrogenase phosphate phosphatase activity - abstract

We have measured the rates of activation of the mitochondrial pyruvate dehydrogenase multi-enzyme complex (PHD) in kidney mitochondria from fed and starved rats. A significant diminution of rate due to starvation was found. The effect of varying Mgý+ concentration on the rate suggests that starvation induced a covalent modification of PDH phosphatase or its substrate which modification impaired dephosphorylation by decreasing its sensitivoty to Mgý+ (AU)

Changes in red cell insulin receptors during recovery from severe malnutrition

Red cell insulin binding was studied in 13 Jamaican children (age range 4-24 months), while malnourished (MAL), during early recovery (GI), late recovery (GII), and after anthropometric recovery (REC). The rate of weight gain (RW), the energy intake (EN), and the protein intake (PR) were monitored at each phase of the study. Four-hour fasting blood samples were used, and the insulin binding characteristics were investigated in the physiological range of insulin concentrations (16.7-1670 pM). Analyses of variance were used to examine differences in the variables measured at the four phases. Red cell-specific insulin binding (SB) was lower in MAL than in GI (P<0.001) and in (GII) (P=0.026). SB in REC and MAL were not significantly different. Insulin receptor affinity (K) was also lower in MAL than in GI (P<0.001), GII (P<0.001), and REC (P=0.012). The insulin receptor number (S) appeared to be high in malnutrition and to decrease as recovery progressed; however, the decrease was not significant. Children with fever demonstrated high insulin binding. Plasma insulin (IN) rose during recovery, and was significantly higher in GII than in MAL (P=0.01). There was no difference in plasma glucose (G) at any phase of the study. The interrelationships among the variables measured were investigated longitudinally using multiple regression analyses. SB was positively associated with S (P=0.032), EN (P=0.029), and PR (P=0.0076). S was negatively associated with K (P<0.001). The associations of S and K with PR were positive and approached significance (P = 0.09 and P = 0.07 respectively). RW was positively associated with PR (P<0.001), and with EN (P=0.001). There were no significant relationships between G and any of the other variables longitudinally. However, correlations of the variables within phases demonstrated that in MAL, G was negatively associated with SB (P<0.05) and with K (P<0.05); but in REC, G was positively associated with SB (P<0.05). These results demonstrated that in severe malnutrition, the red cell insulin receptor affinity was low. During catch-up growth when protein and energy intakes were increased, both insulin receptor affinity and specific insulin binding were also increased. The negative relationship between insulin binding and plasma glucose during malnutrition may be related to carbohydrate intolerance (AU)

The relationship of red cell insulin binding to rate of weight gain during recovery from malnutrition - abstract

Chronic nutrient inadequacy, as exemplified by marasmus and kwashiorkor provides a model for insulin-binding studies. Red cell insulin receptors were studies in infants (age range 4 to 24 months) whilst malnourished and at 3 different stages of anthropometric recovery (60-84, 85-95, and 96-110 percent weight-for-height (EWH)). Four-hour fasting blood samples (3 ml) were used. Washed red cells (concentration 0.75 - 1.5x10 Esp 9/ml) were incubated at 15§C for 180 min in the presence of a constant amount of tracer (A[14] - I[125] - insulin, 16.6 - 1680 pM, 7 different concentrations). Non-specific binding was assessed by the radioactive insulin bound in 10,000 x the physiological range of insulin concentration. From the competitive binding curve, total binding, affinity and number of receptor sites were calculated by Scatchard analysis. Specific insulin-binding was expressed as the per cent of total A[14] -I[125]-insulin added at a cell concentration of 4x10Exp9/ml. Red cell specific insulin-binding (SB) in malnutrition (rate of weight change, (RWC) - 2.05ñ1.9 (10) g/kg/d) was 4.2ñ0.8 (12) percent. This was significantly less than at all three phases of recovery (p<0.01). At 60-84 percent EWH(RWC ñ 11.7ñ0.9 (20)), SB was 8.6ñ1.2 (20) percent: at 96 -110 percent EWH (RWC ñ 0.95ñ1.1 (11)), SB was 8.8ñ1.4 (11) percent. A significantly (p<0.01) lower affinity of insulin for its receptor was shown in malnutrition, 0.9ñ0.2 (12) (Kx10Exp-8 M) than at other phases of recovery, 1.8ñ0.1 (24), 1.6ñ0.2 (20), and 1.4ñ0.4 (11) respectively. There were no significant changes in the number of receptor sites during malnutrition or during the catch-up growth phases. There was a highly significant positive correlation between rate of weight change and specific insulin-binding, (r= 0.45, p<0.0001 (67) as compared with plasma insulin concentration (r=0.33, p<0.01). Specific insulin-binding was also significantly correlated with the affinity of insulin for its receptor 9 r=0.28) p<0.05 (67)). Preliminary Results suggest that decreased protein, but not the carbohydrate or fat content of the diet, was associated with reduced insulin receptor affinity. Chronic nutritional inadequacy alters the affinity of the red cell receptor for insulin, leading to decreased binding, and this is quickly reversed early in rehabilitation. Decreased insulin-binding may be related to the carbohydrate intolerance of severe malnutrition (AU)

Insulin receptor properties in lactating rat mammary gland acini - abstract

Equilibrium binding of 125 I-insulin by lactating rat mammary gland acini was carried out at 4§C for 18 hours. Data were analysed as recommended by Scatchard. Published work on insulin receptors in other tissues generally shows Scatchard plots with an upward concavity. This is interpreted either as two receptor populations of different affinities or one population whose affinity declines with increasing saturation (negative co-operativity). Our data showed a small decline in number of mammary gland receptors when animals were deprived of circulating prolactin. Our Scatchard plots for control, 48-hr starved or prolactin-deprived animals also exhibited a 'shoulder' in the region between free insulin concentrations of 1.1 ng/ml and 2.1 ng/ml (physiological levels). This may indicate a sub-population of receptors exhibiting positive co-operativity (increasing affinity with increasing saturation). There is, to our knowledge, only one similar published report of positive co-operativity of insulin receptors - in rat hepatoma. We are trying to correlate these findings with the known autophosphorylation and aggregation behaviour of insulin receptors. If positive co-operativity of insulin receptors occurs in other tissues, this can have important implications for insulin action and aetiology of diabetes mellitus (AU)

Persistent impairment of insulin secretion and glucose tolerance after malnutrition

Oral glucose tolerance tests on Jamaican children after an average of 3 months treatment in a hospital for malnutrition suggested a diminished peripheral uptake of glucose. This was confirmed with intravenous glucose tolerance tests. Despite 3 months treatment on an optimal diet the children's plasma levels of immunoreactive insulin were still subnormal, and the insulin response to intravenous glucose was much less than in Jamaican children who had never been malnourished. This suggests that malnutrition may produce a permanent reduction in the capacity for insulin secretion (AU)

Preparation and some properties of isolated islets of langerhans from rabbit pancreas

Isolated islets of Langerhans have been prepared by collagenase digestion of rabbit pancreas. These islets are capable of responding with increased insulin secretion to high extracellular glucose concentrations, but show a relatively high "basal" secretion as compared to incubated pancreatic pieces of approximately 1 cm3 surface area. Insulin is not degraded in contact with islets. The cause of the apparently low insulin content per islet requires further investigation (AU)

Some controversial questions concerning the aetiology of diabetes mellitus

In this review the author has adopted a definite position i.e. that there is a single proximate cause or biochemical lesion underlying all cases of diabetes. This, of course, is only a hypothesis but for consistency it was decided to omit consideration of questions like the influence of diet on diabetes since there is at the moment, no indication of how such a factor could be introduced into the current "sub-hypotheses" about aetiology of diabetes. From a practical experimental point of view the conclusions are that useful results may be expected from one or more of the following programmes:- 1. Addition of assays of plasma insulin, NEFA, glycerol and triglycerid to the glucose concentrations as important parameters in assessment of diabetics. 2. Search for circulating lipid mobilizing factors in the blood of diabetics. 3. Biochemical analysis of samples of diabetic fat removed at operation or biopsy e.g. studying properties of A & B chains of insulin and attempts to demonstrate their presence in diabetic plasma. 4. Long term follow up of maintained experimental diabetic "complications" might indicate which of these animals furnishes the best "Model" for human diabetes (AU)

Control of insulin secretion

A simple, reproducible, in-vitro system for studying insulin release from rabbit pancreas was described. It involved the use of a specific and sensitive immunoassay for insulin. Using this system it was shown that of several monosaccharides tested only glucose and mannose stimulated secretion while the sugar manonheptulose inhibited stimulation due to glucose or mannose. Evidence was presented that this later observation indicates the necessity for phosphorylation of glucose within the B-cell prior to stimulation of insulin secretion. Among the hormones tested only adrenaline exerted a significant effect (inhibitory) on insulin release. The antidiabetogenic drug tolbutamide had a marked stimulant effect thus confirming conclusions from indirect evidence. This technique can help to clarify the intra-cellular mechanism of controlled insulin release from B-cells, can be used in deciding the mode of action of proposed anti-diabetogenic drugs and possibly for testing certain hypotheses about the aetiology of diabetes (AU)

Effects of pyruvate on pyruvate dehydrogenase kinase of rat heart

Sensitivity of rat heart pyruvate dehydrogenase kinase (PDHK) to pyruvate inhibition was tested under various conditions using pyruvate dehydrogenase complex (PDC) in mitochondria (mPDC) and in high speed precipitate of whole tissue homogenates (hPDC). In the latter preparation pyruvate in the range of concentration 1-10 mM caused increasing inhibition of PDHK when the enzyme was prepared from animals fed libitum but had no effect when the enzyme was prepared from 48h starved animals. Similiar behavior was observed in mPDC from fed and starved animals when rotenone was present in the incubation medium. When carbonyl cyanide m-chlorophenylhydrazone (CCCP) instead of rotenone was present, pyruvate at 1 mM concentration stimulated PDHK from hearts of fed animals, but was without effect at 10 mM. When mPDC or hPDC from hearts of starved animals was incubated at 30 degrees Celsius for 30 min, inhibition of PDHK by pyruvate was restored (AU)